Field of the Invention
The present invention is particularly concerned with the construction of a so-called pulser employed in anti-lock controls for vehicle braking systems.
When the brakes of a vehicle travelling on a wet or icy road are applied, extreme care must be taken to prevent locking of the wheels with the consequent loss of control of the vehicle. Computerized anti-lock braking control systems have been developed which, by monitoring the rate of rotation of the vehicle wheels will control the action of the vehicle brakes to apply the maximum braking action short of wheel locking even if the driver over brakes.
A typical wheel rate of rotation monitoring device employed in such systems takes the form of a pulser having the general shape of an external gear which is mounted to rotate with the wheel. A sensor is mounted on the vehicle frame adjacent the periphery of the pulser and the teeth of the gear-like pulser rotating past the sensor cause the sensor to generate a pulsating electric signal whose frequency is proportional to the rate of rotation of the wheel. This signal is fed into a computerized control system which, upon application of the brakes, will override the controlling action of the brake pedal to prevent locking. Several types of such systems are commercially available.
The gear-like pulser employed in such systems is conventional coupled to the vehicle wheel by press-fitting the pulser onto the outer race of a flanged wheel bearing, the outer race in turn being fixedly attached to the brake disk or brake drum of the wheel by means of bolts passing through the flange on the outer race. This mounting arrangement presents several problems, and the present invention is directed to avoiding or minimizing the problems outlined below.
The outer race of the flanged wheel bearings referred to above is conventionally constructed as a forged part which requires heat treatment. Because the pulser is to be mounted upon the outer race by a press or force fit, it is necessary that the annular surface of the outer race upon which the pulser is to be fitted be finish machined to precise dimensional tolerances. Because heat treatment causes dimensional changes in the part, final machining cannot be performed until after the heat treating process is completed, and machining of the hardened heat treated part is not only time consuming, but hard on the cutting tool.
Further, the force fit of the pulser upon the outer race exerts a radially directed compressive force on the outer race which can, and frequently does, cause premature failure of the bearing.
The present invention is especially directed to a pulser construction which dispenses with the need for precise dimensional finishing of the outer race and minimizes the radial compressive forces exerted on the outer race by the assemble pulser while providing a firmly fixed mounting of the pulser upon the outer race.